In the past, optically active .alpha.-tocopherol and derivatives thereof which are the 2R,4'R, 8'R isomers of compounds of the formula: ##STR1## have been prepared through isolation from natural sources as vegetable oil. This procedure suffers from many drawbacks due to the fact that the tocopherol content of these oils is very small. Therefore, a great amount of oil must be processed in order to isolate a small amount of natural tocpherol. Additionally, the process whereby various tocopherols are isolated from vegetable oil is extremely cumbersome.
In U.S. Pat. No. 3,947,473 Scott et al., vitamine E active compounds have been synthesized by reacting via a Wittig reaction a compound of the formula:: ##STR2## wherein R is hydrogen or forms an ether protecting group removable by hydrogenolysis or acid catalyzed cleavage. (Please note, the compound of the formula XXVII where n is 1 in U.S. Pat. No. 3,947,473 ) with a phosphonium salt prepared from a compound of the formula: ##STR3##
(Please note, compound XLIV in U.S. Pat. No. 3,947,473 ). Where the compound of the formula III has a 2R, 6R configuration, i.e. a compound of the formula: ##STR4## then natural .alpha.-tocopherol is produced by this procedure.
In accordance with this process, it has been desired to provide a simple and economic method for preparing the compound of formula III and III-A from relatively cheap and economic starting materials.